1. Technical Field
The method and apparatus of the invention relate generally to a means for maintaining a preselected track through crop rows, furrows or the like for agricultural vehicles such as a tractor, cultivator or the like. More specifically, it relates to an apparatus and method of using a dual ultrasonic transducer to detect lateral displacements from a predetermined track between two crop rows, furrows, plowing marker furrows or the like. Throughout, this specification, furrows will be meant to include also crop rows, marking furrows and the like. Further, any signal error from vertical displacement of the vehicle is eliminated by use of the dual transducer system to produce a signal verification. Additionally, any noise generated from various debris in the path of the vehicle is filtered out.
This invention is documented in Disclosure Document No. 303806 received in the Patent and Trademark Office on Mar. 10, 1992.
2. Description of the Prior Art
Several techniques have been suggested in the prior art for allowing a tractor or other agricultural vehicle to avoid obstacles or maintain a specified vertical separation with the ground. One example of such a prior device is Ito et al., U.S. Pat. No. 4,537,271, which describes a non-contact type obstacle sensor mounted on the front portion of a running vehicle. The sensor determines whether an obstacle detected ahead of the vehicle is moving or stationary. If the obstacle is stationary, the vehicle is turned so as to cause it to detour around the obstacle. If the obstacle is in motion, the vehicle is stopped. The preferred sensor of this invention is a photo sensor which is used to emit a beam of light and then to detect the reflection of the light from the obstacle.
Another example of a prior art device is Phelan, U.S. Pat. No. 5,060,205, which describes a distance sensing system including an ultrasonic transducer, a transceiver and a micro controller-based signal processing unit. The device measures a vertical distance between the terrain and the sensor, and is not used for determining a lateral displacement measurement for use in controlling the tracking of a vehicle down a desired path.
A problem previously encountered with these types of devices for use with automated guidance systems, was that the ultrasonic sensor being much more sensitive to field debris, would transmit any and all debris (i.e., clods, plant stalks, etc.) in addition to the furrow surface. The output signal was essentially useless, due to the amount of random noise caused by this debris. Additionally, many of these devices may only be used with that manufacturer's equipment.
Several manufacturers have supplied steering guidance systems for agricultural vehicles wherein the wheels of the vehicle may be turned based on a variable voltage or current input to the guidance system. Several devices have been developed to generate this variable voltage for the guidance systems. Generally, these devices comprise mechanical potentiometers which sense when a tracking wheel has deviated from the predetermined path. The potentiometer sends a variable voltage to the vehicle's guidance steering system which in turn activates a mechanical linkage to move the wheels, thereby correcting the deviation. A major drawback of this type of system is the mechanical nature of the translation from lateral displacement to steering commands through the potentiometer. Another drawback is the precision with which the potentiometer is able to change values. Potentiometers are also generally fragile and tend to wear out quickly. Further, these systems can generally only be used with that manufacturer's equipment.
Another means of providing steering signals to agricultural vehicles is through heavy and cumbersome ground sensors which travel along the bottom and middle of the row. These sensors utilize freely moving "rabbit ear" mechanical feelers or heavy metal "balls" connected to a potentiometer or Hall-effect transducer in the center, rotating laterally as the ridges move closer or farther. The user sometimes will try to back up with the vehicle, and "hook" the reversed-angle feelers or metal balls on plant stalks or the ridge itself and either bend or break the otherwise fragile feelers or balls.
None of these prior art devices teach the unique apparatus and method of the present invention whereby a tractor or other agricultural vehicle is able to maintain a constant preselected track through a crop row and to filter out debris detection and vertical movements of the vehicle caused by bumps in the track.
Accordingly it is a primary objective of the present invention to provide an apparatus which is capable of maintaining a constant preselected desired track through crop rows, furrows, plowing mark furrows or the like, thereby allowing the tractor or other agricultural vehicle to track down a crop row, furrow or plowing mark furrow.
Another object of the present invention is to provide an apparatus which is capable of filtering out any signal noise generated by debris and the like, providing a valid signal indicative of the furrow surface, plant stalk bottom or crop row.
Another object of the present invention is to provide an apparatus which is capable of discriminating between valid lateral movements of the tractor or vehicle and invalid vertical movements caused by bumps in the crop row or the like.
Still another object of the present invention is to provide an apparatus which may be utilized with existing guidance control equipment utilizing a variable input voltage or current to control steering of the vehicle's wheels, present on many of today's agricultural vehicles.
Another object of the present invention is to provide an apparatus which is capable of using off-the-shelf transducer sensors.
A final objective of the invention is to provide an apparatus which is simple and inexpensive yet able to accomplish the above mentioned objectives.